Synchronizing system



L. ESPENSCHIED.

SYNCHHONIZING SYSTEM.

APPLicATloN FILED senso. 1919.

N m w P M S m.

IN VEN TOR.. L. f/wilffald BY A TTRNEY UNITED STATES PATENT OFFICE.

LLOYD ESIENSCHIED, OF HOLLIS, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONEAND TELEGRAPH. COMPAN Y, A CORPORATION OF NEW YORK.

sYNcHnoNTzINe sYsrmE Specification of Letters l'atent.

Patented Apr. 18, 1922.

Application led September 30, 1919. Serial No. 327,504.

To all whom it may concern Be it known that I, LLOYD EsrENscHIno,residing at Hollis, in the county of Queens and State of New York, haveinvented certain Improvements in Synchronizing Systems, of which thefollowing is a specificau tion.

This invention relates to signaling circuits and more particularly toarrangements for maintaining synchronism between alternating vcurrentsseparately generated at different stations of a signaling system.

011e of the features of the invention resides in the provision of meanswhereby alternating currents supplied from two independent sources maybe automatically maintained at the same frequency.

Another feature of the invention resides in the provision of meanswhereby alternating currents supplied at the receiving station of asignaling systemV may be maintained in synchronism with carrier currentsreceived from a distant sending station.

These features, together with other features more fully hereinafterappearing, are realized in the arrangements set forth in the followingdescription and illustrated in the accompanying drawing, the figure ofwhich constitutes a circuit diagram of one embodiment of the invention.

Referring to the drawing, AR designates a receiving antenna'of anyordinary construction, which is coupled through a transformer 1, with atuned circuit 2, resonant lat the desired received frequency. Areceiving circuit TL is associated with the tuned circuit 2 and includesa demodulating or detecting apparatus D, a filter F, an amplifier A anda receiver R. The detector D may be of any well known type, but ispreferably a vacuum tube detector operating upon the so-calledhomodyneprinciple of receiving and is therefore supplied with homodynecurrents over a circuit 3, in a manner hereinafter described. Thesehomodyne currents should be of the same frequency as the receivedcarrier frequency upon which' the signal is superposed, so that the lowfrequency currents corresponding to the signal will appear in the outputcircuit of the demodulator. The filter F may be of any well known type,but is preferably a band filter of the type disclosed in the U. S.patents to George A. Campbell, Nos. 1,227,113 and 1,227,114, issued May22, 1917, and is designed to suppress higher frequencies, while inpractice vary slightly in frequency from the received carrier frequency.In order that the oscillations supplied to the circuit 3 as the resultof the action of the generator G1, may be of the same frequency as thereceived carrier frequency, a series of modulating and filteringarrangements are provided.

This combination of devices includes modulators M M2, M3, M4, M5 and M6,arranged 1n a circuit 4, branched from the .tunedcircuit 2.v Thesemodulatorslmay be`of any well known type, but are preferably vacuum.

tube modulator-s. Filtering arrangements, such as F F2, F3, F4, F5 andF6, are ineluded in the'output circuit of the corresponding modulators,for a purpose more fully hereinafter described. These filters may alsobe of the type disclosed in the above mentioned patents to George A.Campbell, and are designed to transmit one of the side bands resultingfrom modulation, to the eir-y .clusion of the other.

- The modulator M1 is supplied with modulating current rfrom the sourceG1, over a circuit 5. The modulator M2 is in a similar manner suppliedwith modulating current from a source G2, over a circuit 6. So also, themodulator M3 is supplied with modulating current from a source G3, overthe circuit 7, while the modulator M, is supplied from a source G4, overa circuit 8. The modulator M5 is supplied with modulating current over acircuit 9, leading from the generator G1.

In order to supply modulating current for the modulator Me, a circuit 10is rovided, which includes modulators M', and p 4, similarv to thosealready described, and ineluding filters F3 and F4in the output circuitsof the modulators respectively. The modulator M3 is supplied withalternating our; rent from the source G2, over a circuit 11 and 'is alsosupplied from the source G, over` the circuit 12. The resultant sideband selected by the filter F 1, is then supplied to the modulator M1,which is also supplied with oscillating current from the source G1, overa circuit 13.

Further details of the apparatus may now be understood from a.description of the operation, and in order to facilitate thedescription, a concrete set of frequencies will lbe assumed, although itwill be understood that these frequencies are referred to merely forpurposes of illustration. If the modulated carrier current received bythe antenna AR has a frequency of 100,000 cycles, together with the sideband resulting from modulation, it is necessary for the most efficientdetection` that the detector D should be supplied with a homodynefrequencyv of 100,000 cycles. Normally this frequency would be suppliedby the local generator G1. This generator, however, may supply a carrierfrequency slightly different from that desired. For instance, thefrequency supplied by the generator G1 may be 100,005 cycles. Thisfrequency is supplied to the modulator M1 over the circuit 5, while thecarrier frequency of 100,000, together with the side band frequencies,are supplied to the modulator M1 over the circuit 4. As a result of themodulating action of the modulator M1, frequencies corresponding to thesums and differences of the frequencies supplied to the input of themodulator, will appear in the output circuit of the modulator,consequently a frequency of 5 cycles, corres spending to the differencebetween 100,000 and 100,005 will appear in the output circuit of themodulator M1. The filter F1, which is preferably a low pass filter, maybe accurately designed to select this frequency and exclude the higherfrequencies. 1

f we assume the frequency supplied by the generator G2 to the modulatorM2 to be 100 cycles, this frequency will be modulated by the five cyclefrequency transmitted to the modulator M2 from the filter F1, so that bycombining the frequencies, the output circuit of the modulator will besupplied with frequencies of 95 and 105 cycles, respectively. The latterfrequency may be selected by the filter F1, which is preferably a highpass filter, so as to exclude the lower frequency. This frequency issupplied to the modulator M3, to ether with a frequency from thegenerator 3, which latter may be, for instance, 1000 cycles. As a resultof the action of the modulator M3, a frequency of 1105 cycles will nowappear among others in the output circuit of. the modulator Mw Thisfrequency may be selected by the high pass filter F3 and supplied to themodulator M1. The modulator MA1 is supplied with a frequency of 10,000cycles from the generator G1, so that as a result of its modulatmgaction a frequency of 11,105 cycles will appear in its output circuit asthe upper side frequency. This frequency may be selected from the lowerside frequency and the 10.000 cycle frequency, by means of the filterF4, so that a frequency of 11,105 is now supplied to the modulator M5.At the same time a frequency of 100,005 is supplied to the modulator M5from the generator G1, over the circuit 9. Among the frequenciesresulting from the modulation of these two frequencies by the modulatorM5, the filter F5 may select the frequency corresponding to the lowerside frequency, which will be 88.900 cycles. This frequency is nowsupplied to thc modulator M6.

Returning now to the modulator M21, frequencies of 100 cycles and 1,000cycles are supplied to said modulator over circuits 11 and 12,respectively. The sum of these frcquencies` which, of course, resultsfrom the modulatingv action of the modulator M21, may be selected to theexclusion of the lower side band, by means of the filter F This sumcorresponds to a frequency of 1100 cyclesfwhich is supplied to themodulator M1, together with a frequency of 10,000 cycles from thegenerator G1. The modulating action of this modulator produces sum anddifference frequencies, as before, of which the former, corresponding toa frequency of 11,100 cycles, may be selected by thc filter F4 andtransmitted over the circuit 10 to the modulator MG.

The modulator Mn is consequently supplied with currents havingfrequencies of 88,000 and 11,100, which, when combined in the modulator,produce a frequency of 100,000 cycles, as well as lower frequencies.The.f'requency of 100,000 cycles may be selected by the filter F6 andsupplied over the circuit 3 to' the demodulator D. 1t will be noted thatthis frequency of 100,000 cycles has exactly the same frequency as thereceived carrier frequency, even though the generator G1 varies fromsaid carrier frequency, and this will hold true however the frequency ofthe generator G1 may vary, at least Within limits. The detector D, uponbeing supplied with the beating frequency of 100,000 cycles, detects thelow frequency signaling currents in a Well known manner and thesecurrents are passed through the filter F, amplified by the amplifier Aandthen operate the receiving instrument R.

The frequencies above referred to are, of course, merely illustrativeand may be varied as conditions may require. It will also be obviousthat the general principles herein disclosed may be embodied in manyother organizations Widely different from those illustrated, withoutdeparting from the spirit of the invention as defined in the followingclaims.

What is claimed is:

l. The method of synchronizing two frequencies which consists incombining the two frequencies so as to produce a frequency correspondingto ltheir difference, stepping up the difference in the frequencyspectrum a predetermined amount, combining the stepped up frequency withone of the frequencies to be synchronized and producing from theresultant frequency a frequency corresponding to the other frequency tobe synchronized.

2. The method of synchronizing two frequencies which consists incombining the two frequencies so as to produce a frequency correspondingto their difference, stepping up the difference frequency in thefrequency spectrum by a predetermined amount, combining the stepped upfrequency with one of the frequencies to be synchronized and combiningthe resultant frequency with another frequency equal to the amount bywhich the difference frequency was stepped 3. The method ofsynchronizing two frequencies which consists in combining the twofrequencies so as to produce a frequency corresponding to theirdifference, subjecting the difference frequency to a beating action withat least one other locallysup'plied frequency, thereby producing afrequency de,-

termined by the difference frequency but higher in the frequencyspectrum,combin ing the resultant frequency with one of the frequenciesto be synchronized and then beating the combined frequencies withanother frequency to produce a frequency corresponding to the otherfrequency to be synchronized. i

4. The method of synchronizing two frequencies which consists incombining the two requencies so as to produce a frequency correspondingto their difference, subjecting the differency frequency to successivebeating opera-tions to produce a frequency determined by said differencefrequency but higher in the frequency spectrum, combining the resultantfrequency with one of the frequencies -to be synchronized and thencombining the resultant frequency with a frequency differing from thefrequency derived from the difference frequency by an amount equal tothe difference frequency.

5. In a synchronizing system, a modulator, means to supply to saidmodulator two frequencies which are to be synchronized, means to selectthe dierence frequency from said modulator, apparatus to step up saiddiHerence frequency in the frequency spectrum by a predetermined amount,a second modulator, means to impress said stepped up frequency and oneof the frequencies to be synchronized upon said second modulator, andmeans to derlve from the resultant frequency a frequency correspondingto the other frequency to be synchronized.

6. In a synchronizing system, a modulator, means' to supply to saldmodulator two frequencies which 'are to be synchronized, means to selectthe difference frequency from said modulator, means to step up saiddifference frequency by a predetermined amount through a succession ofbeating operations, a second modulatorymeans to impress said stepped upfrequency and one of the frequencies to be synchronized upon said secondmodulator, means to select the resultant difference frequency from themodulator, means to produce a frequency differing from said stepped upfrequency by an amount equal to the original difference frequency, athird modulator and means to apply the frequency thus produced and thefrequency selected from the second modulator to said third modulator,thereby producing a frequency corresponding to the other frequency to besynchronized.

In testimony whereof Ihave signed my na'me to this specification this29th day of September 1919.

LLOYDK ESPENSCHIED

